Factors Involving Potential and Kinetic Energy

Name: ______

Period: ______Date: ______

FACTORS INVOLVING POTENTIAL AND KINETIC ENERGY

POTENTIAL and KINETIC ENERGY are both forms of MECHANICAL ENERGY. In the experiments below, you will measure the potential and kinetic energy of a lab cart. Once the initial data has been recorded, you will conduct experiments to investigate the factors which have the greatest impact on the two forms of mechanical energy.

MATERIALS:

stop watch meter stick books ramp 500g mass pieces Newton scale cart masking tape

PROCEDURE:

A. Use the Newtons scale to measure the mass of the cart in kilograms (kg) and the weight in Newtons (N). Record these values in TABLE 1.

B. Construct a 0.2 meter incline for the ramp by stacking several books. Verify the height is 0.2 meters from the floor to the top of the incline by measuring with a meter stick.

TABLE 1 VELOCITY AT MASS OF WEIGHT OF POTENTIAL KINETIC HEIGHT (m) BOTTOM OF CART (kg) CART (N) ENERGY (J) ENERGY (J) RAMP (m/s)

C. Calculate the potential energy of the cart at the top of the incline using the formula below. Since the cart was measured using the Newton scale, the effects of gravity have been accounted for and the weight of the cart is represented in Newtons (N).

POTENTIAL ENERGY = WEIGHT x HEIGHT

Remember: Units for potential energy are Joules (J) Units for weight are Newtons (N) Units for height are meters (m)

1 D. Since kinetic energy is dependent on the velocity of an object, some experimental data of the cart’s velocity must be gathered. Place the cart at the top of the incline and measure the time it takes to reach the bottom of the ramp using a stop watch. Record this value in TABLE 2. Repeat this procedure two more times and record the data.

E. The distance the cart travels is the length of the ramp. Measure the length of the ramp in meters and enter the distance in TABLE 2. This distance should be identical for all three trials.

TABLE 2 AVERAGE TRIAL TIME (s) DISTANCE (m) VELOCITY (m/s) VELOCITY (m/s)

F. The velocity for each trial can be calculated by dividing the distance traveled by the time taken to reach the bottom of the ramp. The units for velocity are in meters per second (m/s).

Distance Velocity = Time

G. Calculate the average velocity of the three trials and record this value in TABLE 2.

H. Since the cart is accelerating smoothly, the velocity at the bottom of the ramp is just twice the average velocity. Use this fact to calculate the velocity of the cart at the bottom of the ramp and record this value in TABLE 1.

Velocity at bottom of ramp = 2 x Average velocity

I. Calculate the kinetic energy of the cart at the bottom of the ramp by using the formula below. Make sure you use the velocity at the bottom of the ramp when evaluating the expression. Record the value of the kinetic energy in TABLE 1.

KINETIC ENERGY = (0.5) x MASS x VELOCITY2 KE  (0.5)*mv2

Remember: Units for kinetic energy are Joules (J) Units for mass are kilograms (kg) Units for velocity are meters per second (m/s)

2 PREDICTIONS AND HYPOTHESIS:

CASE 1. How do you think a change in mass will affect the cart’s potential and kinetic energies?

Your predictions (circle all that apply):

A change in mass will affect:

POTENTIAL ENERGY KINETIC ENERGY NEITHER

An increase in mass will cause the potential energy to:

INCREASE DECREASE NO CHANGE

An increase in mass will cause the kinetic energy to:

Briefly state why you made the predictions above.

CASE 2. How will a change in the height of the ramp affect the potential and kinetic energies?

A change in height will affect:

POTENTIAL ENERGY KINETIC ENERGY NEITHER

An increase in height will cause the potential energy to:

An increase in height will cause the kinetic energy to:

Briefly state why you made the predictions above.

3 TESTING OF HYPOTHESES Now that your hypotheses have been made predicting the impact of changes in mass and height on the kinetic and potential energies, you are ready to test them. When testing hypotheses, it is crucial that all variables remain constant except for the one that is being tested. Since you are interested in the effects of mass and height on the energies, two separate experiments must be conducted to produce reliable results. The first set of experiments will examine the effects of mass, and the second set of experiments will focus on changes in heights.

CHANGE IN MASS: A. Since the mass is the variable of interest in the following experiments, all other factors including the ramp height will remain constant. Copy the original experimental results that were recorded in TABLE 1 to the first row of TABLE 3 for comparison. Recall that this experiment involved the cart without any masses at a height of 0.2 meters.

B. Place ONE 500g mass on the cart and repeat the original experiment for determining the potential and kinetic energies. Record your data in row two of TABLE 3. Use TABLE 4A to record the velocities and to determine the average velocity of the three trials.

TABLE 3 VELOCITY AT DESCRIPTION MASS OF WEIGHT OF POTENTIAL KINETIC HEIGHT (m) BOTTOM OF OF CART CART (kg) CART (N) ENERGY (J) ENERGY (J) RAMP (m/s)

Cart only 0.2 m

Cart with one 0.2 m mass

Cart with two 0.2 m masses

Remember that the velocity at the bottom of the ramp is twice the average velocity.

TABLE 4A MASS OF CART AND ONE MASS:______

AVERAGE TRIAL TIME (s) DISTANCE (m) VELOCITY (m/s) VELOCITY (m/s)

4 C. Place TWO 500g masses on the cart and repeat the original experiment for determining the potential and kinetic energies. Record your data in row three of TABLE 3. Use TABLE 4B to record the velocities and to determine the average velocity of the three trials.

TABLE 4B MASS OF CART AND TWO MASSES:______

AVERAGE TRIAL TIME (s) DISTANCE (m) VELOCITY (m/s) VELOCITY (m/s)

CHANGE IN HEIGHT: A. Remove all masses from the cart. The factor of interest is the height of the ramp. All factors will remain constant for each of the following experiments except for the height of the ramp. The mass used for the following experiments will be only the cart with no additional masses. Data will be recorded for ramp heights that are both greater and lower than the original ramp height.

B. Copy the original experimental results that were recorded in TABLE 1 to the first row of TABLE 5 for comparison. Recall that this experiment involved the cart without any masses at a height of 0.2 meters.

C. Repeat the original experiment for a ramp height greater than the original ramp height, but do not exceed a height of 0.5 meters. Store the results in row two of TABLE 5. Use TABLE 6A to record the velocities and to determine the average velocity of the three trials.

TABLE 5 VELOCITY AT DESCRIPTION MASS OF WEIGHT OF POTENTIAL KINETIC HEIGHT (m) BOTTOM OF OF CART CART (kg) CART (N) ENERGY (J) ENERGY (J) RAMP (m/s)

Cart Only 0.2 m

Cart only

Cart Only

5 TABLE 6A HEIGHT OF RAMP:______AVERAGE VELOCITY TRIAL TIME (s) DISTANCE (m) VELOCITY (m/s) (m/s)

D. Adjust the height of the ramp to a height that is less than the original ramp height. Repeat the original experiment and store the results in row three of TABLE 5. Use TABLE 6B to record the velocities and to determine the average velocity of the three trials.

TABLE 6B HEIGHT OF RAMP:______AVERAGE VELOCITY TRIAL TIME (s) DISTANCE (m) VELOCITY (m/s) (m/s)

6 ANALYSIS AND RESULTS: 1. What factor (mass or height) has a greater impact on potential energy? What experimental evidence have you gathered from this lab that supports your decision?

______

2. What factor (mass or height) has a greater impact on kinetic energy? What experimental evidence have you gathered from this lab that supports your decision?

______

3. Now that you have completed the lab, how would you increase the potential energy of the cart without changing the mass of the cart?

______

4. In general, how did the cart’s potential energy at the top of the ramp compare with its kinetic energy at the bottom of the ramp?

______

5. While riding a bicycle, roller blading, skiing or skate boarding you may have noticed that you travel faster down large hills and slower down smaller hills. Explain why.

______